1. Field of the Invention
The invention relates to a driving method using a motor, a driving apparatus using a motor, an exchanging apparatus of a recording medium, and a driving method of an exchanging apparatus of a recording medium.
2. Description of the Related Art
A disk exchanging apparatus such that a plurality of optical disks such as CD-ROMs are enclosed in a disk enclosure and a desired optical disk is taken out from the disk enclosure and is loaded into a disk driving apparatus has been developed.
That is, such a kind of disk exchanging apparatus comprises: the disk enclosure in which a plurality of disks are enclosed; an elevator for conveying the disk from the disk enclosure to the disk driving apparatus or from the disk driving apparatus to the disk enclosure; and the disk driving apparatus. When a desired disk is designated from a plurality of disks, the elevator is moved to a slot in which such a disk is enclosed, and the disk is taken out of the slot. The disk is conveyed to the disk driving apparatus by the elevator and is loaded into the disk driving apparatus.
In case of exchanging the optical disk in the disk driving apparatus, the elevator is moved to the position of the disk driving apparatus and the optical disk is taken out from the disk driving apparatus. The ejected optical disk is conveyed by the elevator to the slot corresponding to the original enclosing position of the disk enclosure and is enclosed into the slot. The elevator is subsequently moved to the slot in which a new optical disk is enclosed, the optical disk is taken out of the slot, and the optical disk is conveyed to the disk driving apparatus and is loaded into the disk driving apparatus.
In such a kind of disk exchanging apparatus, another disk exchanging apparatus such that a plurality of disks are enclosed in the disk enclosure in parallel in the vertical direction, a motor is arranged in the elevator, and the elevator is driven in the vertical direction by a motive power of the motor in the elevator has also been proposed. It is considered to use a stepping motor as a motor to move the elevator.
However, since there is a variation in angle of rotation per step of the stepping motor, it is difficult to control the position of the elevator by the stepping motor at high precision.
That is, if a relation between the rotational angle of the stepping motor and the number of steps is ideal, in such a disk exchanging apparatus, a movement amount of the elevator to the number of steps linearly changes. However, there is a variation in the rotational angle per step of the stepping motor. That is, in the stepping motor, although positioning precision is determined by the number of steps of the motor denoted in a motor body, if there is a variation in dimensions of an internal magnetic circuit, a detent torque (holding power when a coil is open) varies. In case of the magnetic circuit of a multilayer structure, a magnitude of a lead angle appears as a tendency-like difference in the even-number steps and the odd-number steps.
Due to such a variation in rotational angle per step of the stepping motor, the relation between the rotational angle of the stepping motor and the number of steps does not become linear. An error occurs due to such a variation in rotational angle per step and it is difficult to position at high precision.
The angle of rotation of the stepping motor is decided by the number of steps and a driving voltage of the stepping motor is hitherto constant. In the conventional disk exchanging apparatus in which the elevator is vertically moved as mentioned above, the driving voltage is determined so as to generate an enough torque by the operation which needs the maximum operating power during the operation of the elevator. That is, since the maximum torque is needed when the elevator is elevated, the driving voltage is set so that enough torque can be held when the elevator is elevated.
However, if the driving voltage of the stepping motor is set so as to generate an enough torque by the operation when the elevator is elevated, this torque becomes an excessive torque in case of lifting down the elevator. According to the construction such that the elevator is vertically moved as mentioned above, it is necessary to apply a torque of a certain degree to the stepping motor even when the elevator is stopped so as to prevent the elevator from dropping. If the driving voltage of the stepping motor is set so as to generate enough torque by the operation when the elevator is elevated, such a torque becomes an excessive torque even when the elevator is stopped.
As mentioned above, when a plurality of disks are arranged in the vertical direction and the elevator is driven by the stepping motor so as to drive the elevator in the vertical direction, according to the conventional driving circuit in which the driving voltage is constant, there are problems such that a lack of torque occurs when the elevator is elevated, a high speed access cannot be performed, the driving voltage becomes an excessive voltage when the elevator is lifted down or stopped, the motor coil generates a heat, and a damage or a deterioration in operating power occurs.
However, in the foregoing disk exchange apparatus, if a power source is suddenly turned off or a power failure occurs, the power supply to the motor is suddenly stopped. Therefore, when the power supply is stopped, the torque of the motor is extinguished and the elevator drops by a self weight or the like, so that a mechanical portion of the disk exchanging apparatus as well as the elevator is broken or causes a fault.